SOI (Semiconductor-on-Insulator) CMOS (Complimentary metal-oxide semiconductor) technology can provide high performance devices, such as field effect transistors (FETs).
Flash memory is a non-volatile memory that can be electrically erased and reprogrammed multiple times. As flash memory is non-volatile, there is no need to have power to maintain the information stored in the chip. Also, flash memory, when packaged in, for example, a “memory card”, is very durable. For these reasons, flash memory has gained popularity in the use of memory cards and USB flash drives for storage and transfer of data. Flash memory has also become the dominant technology wherever a significant amount of non-volatile, solid state storage is needed. For example, flash memory is used in many common devices such as gaming consoles, digital cameras, laptop computers, digital audio players, and mobile devices.
In traditional stacked flash memory, each memory cell includes two gates, e.g., a bottom floating gate and a top control gate. The floating gate is disposed above a channel and is completely insulated about its periphery by an oxide layer. That is, an insulator layer is provided at the interface between the channel and the floating gate, as well as between the interface of the floating gate and the control gate.
A single poly non-volatile random-access memory (NVRAM) has been used to provide non-volatile memory functionality integrated with standard CMOS processes, however these single-poly NVRAM techniques typically occupy more chip area. Thus, providing both high performance FETs and NVRAM devices on the same chip while maintaining high NVRAM density is challenging using conventional methods.
It would be desirable to provide a cost-effective structure and method to integrate both SOI CMOS devices and higher density NVRAM devices on a single chip.